The Immune System

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The Immune System

• The immune system is a bodywide network of cells
  and organs that has evolved to defend the body
  against attack by foreign invaders

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Organs of the Immune System

• Skin and other epithelial surfaces
• Bone Marrow
• Lymphoid Organs

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Skin and Other Epithelial Surfaces a
preventative barrier

• Low pH (3 to 5) due to secretions from oil and
  sweat glands inhibits bacterial growth
• Low pH of urine prevents urinary tract infections
• The proteolytic enzyme, lysozyme, which digests
  bacterial cell walls, is secreted by many
  epithelial cells and sweat glands
• Mucous secretions trap pathogens

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Epithelial Lining of Respiratory Tract

• Lining of the trachea
• Mucous secreting cells
• Ciliated cells

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Bone Marrow Generation of immune cells
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The Human Lymphatic System
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Figure 43.1 An overview of the body's defenses
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The Immune Reaction
If an organism is able to penetrate the skin (the
first line of defense) an immune response is
triggered. You can simulate an immune reaction
by stroking the skin with a pointed instrument.
You will soon see a red reaction due to capillary
dilation, swelling (wheal) due to increased
permeability of the capillaries, and the
spreading (flare) due to arteriolar dilation.
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The Nonspecific Response The Leukocytes

• Phagocytic Cells
• Monocytes and Macrophages
• Neutrophils

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Monocytes and Macrophages

• Monocytes circulate in the blood and when they
  migrate into tissue they develop into
  macrophages. They represent about 5 of while
  blood cells
• The macrophages are large, irregularly shaped
  cells that engulf microbes (phagocytosis)
• The phagocytic vesicles fuse with intracellular
  lysosomes.
• The lysosomes contain the enzyme lysozyme and
  enzymes which generate reactive oxygen species
  (superoxide and nitric oxide), which oxidize the
  microbes.
• Macrophages are important in the activation of
  T-cells

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Figure 43.3x Macrophage
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Figure 43.3 Phagocytosis by a macrophage
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Neutrophils

• 60-70 of all white blood cells.
• Neutrophils have a dual personality. They are
  both phagocytes and granulocytes
• Granulocytes, such as neutrophils contain
  granules filled with potent chemicals, such as
  superoxide (the cellular equivalent to household
  bleach)
• When neutrophils degranulate they kill bacteria
  in the area as well as themselves.

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Figure 43.x1 Anabaena phagocytosed by a human
neutrophil
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The Nonspecific Response The Leukocytes

• Phagocytic Cells
• Monocytes and Macrophages
• Neutrophils
• Natural Killer Cells
• Cytotoxic T-cells
• NK cells

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Natural Killer cells

• NK Cells
• NK cells do not attach microorganisms directly
  instead they destroy virus infected host cells.
• They release perforins, which insert into the
  membrane of the host cell. This pore allows
  water to rush in and burst the cell.
• Cytotoxic T-cells
• These cells function similarly to NK Cells. They
  release proteins that create holes in the host
  cell membrane. Instead of perforins, the
  proteins are complement proteins.

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The Nonspecific Response The Leukocytes

• Phagocytic Cells
• Monocytes and Macrophages
• Neutrophils
• Natural Killer Cells
• NK Cells
• Cytotoxic T-cells
• Granulocytes
• Neutrophils
• Eosinophils
• Basophils
• Mast Cells

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Granulocytes

• Granule containing cells that are filled with
  potent chemicals
• Histamine - released by basophils (circulating)
  and mast cells (connective tissue)
• Histamine causes both dilation and increased
  permeability of nearby capillaries
• Prostaglandins - release by most leukocytes
• Prostaglandins cause the pain and fever
  associated with injury

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Specific Immunity

• Antigen
• Epitope
• Antibody

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Specific Immunity

• Antigen
• Any substance capable of triggering an immune
  response (bacteria, virus, or even a piece of an
  invader)
• Epitope
• Distinctive regions of the antigen that are
  recognized by the immune system
• Antibody
• The antigen receptor

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Lymphocytes that Provide Specific Immunity

• T-cells
• Lymphocytes made in the thymus gland
• B-cells
• Lymphocytes made in the bone marrow (no B does
  not stand for bone marrow - it stands for bursa.
  The bursa is the organ in chicken that makes
  B-cells)

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Review Questions

• Why is the skin an effective first line of
  defense?
• What is the difference between an antigen and
  epitope?
• What causes a fever? Are fevers harmful or
  beneficial?
• What is the difference in the way a NK cells and
  macrophage rid the body of pathogens?